Variable condenser and component



Nov. 2, 1954 e. T. KODAMA VARIABLE CONDENSER AND COMPONENT Filed May 10, 1951 JNVENTOR.

650965 I KODAMA HIS A 7 TOR/V15 Y United States Patent VARIABLE CONDENSER AND COMPONENT George T. Kodama, Mountain View, Calif., assignor to Sprague Electric Company, North Adams, Mass., a corporation of Massachusetts Application May 10, 1951, Serial No. 225,500

4 Claims. (Cl. 317249) The present invention relates to variable condensers, more particularly those types of variable condensers which are of diminutive size and can be used for trimming, that is making small capacitive adjustments in electronic circuits.

Among the objects of the present invention is the provision of a novel variable condenser of improved and simple construction.

Further objects of the invention include the provision of variable diminutive condensers that are sufficiently moisture proof for use under high voltage conditions, and operate very smoothly.

The above as well as additional objects of the present invention will be more completely understood from the following description of several of its exemplifications, reference being made to the accompanying drawings wherein:

Fig. 1 is a perspective view of one form of variable condenser exemplifying the present invention;

Fig. 2 is a bottom view of the variable condenser of Fig. 1;

Fig. 3 is an elevational view of the condenser of Figs. 1 and 2 partially in section as indicated by section line 33 in Fig. 2; and

Figs. 4 and 5 are side views illustrating different methods of mounting the variable condenser of Figs. 1, 2 and 3.

According to the present invention a variable condenser is provided by a rigid dielectric plate, a first electrically conductive stratum held on one face of the plate, and a second electrically conductive stratum pressed against the other face of the plate by an elastically flowable pressing member. An adjusting structure is connected to resiliently bias and adjustably hold the pressing member against the dielectric plate for movement to vary the capacitive opposition of the two electrically conductive strata. The elastically flowable pressing member can conveniently be a disc or sheet of elastomer material such as synthetic or natural rubber which acts as an effective moisture 1mpervious seal and in addition provides a smoothly gliding adjusting movement that is substantially free of abrasive wear. The dielectric plate and pressing member can be pivotally engaged with the pressing member adherently held on a backing disc and rotatably driven by a combined drive and resiliently compressing member having a sheet spring metal body with a plurality of arms extending out generally radially from the body for resilient engagement with the backing member, and a plurality of manipulatable wings extending away from the backing member.

In the construction of Figs. 1, 2 and 3 the capacitor dielectric is indicated as the plate having its lower surface 11 coated with sections 12, 14 of an electrically conductive stratum such as a layer of silver or other suitable metal. Where the dielectric plate 10 is of a ceramic nature, the conductive sections 12, 14 are readily applied in the form of metal paints which can be fired in place to leave a suitable conductive film. Such applications are well known in the art and examples are more fully described in the National Bureau of Standards Circular 468, issued November 15, 1947, pages 5, 6, 7 and 9 to 14 inclusive.

The upper surface 18 of plate 10 is in contact with an elastically flowable pressing member 20 shown as a rubber sheet adherently held on a rigid backing member 22. The plate 10, pressing member 20 and backing 22 are all provided with'central apertures through which is threaded a hollow eyelet 24. The eyelet has a lower head 26 which engages the lower face of plate 10 by way of an intervening insulating washer 28. The upper end of eyelet 24 is also headed over as indicated at 30, and between head 30 and backing plate 22 a compressing spring 32 is mounted to effect the desired compressing engagement of rubber sheet 20 against the plate 10.

In the form shown the spring 32 is a sheet spring metal stamping having a plurality of generally radially directed arms 34 that are bowed or arched to present a concave surface toward the backing plate 22. At least one of the arms carries a hook 36 received in a suitably located and closely fitting socket 38 of the backing plate. The spring 32 is also provided with winged extensions 40 that project upwardly away from the backing plate 22 and provide convenient manipulating elements for rotating the rubber sheet 20 with respect to the dielectric plate 10.

As more clearly shown in Fig. 2, the lower surface of rubber sheet 20 carries sections 42, 44 of an electrically conductive stratum which can be provided in the manner shown in the above-identified National Bureau of Standards Circular using a conductor paint having a processing temperature low enough not to damage the rubber. Sections 42, 44 are preferably made as extensive as possible and may have shapes substantially identical with those of sections 12, 14. In this form of the invention connecting terminals 46, 48 for the condenser are conveniently applied as by soldering to conductor sections 12, 14.

As will be clear from the figures, the capacitance between sections 12, 14 can be subjected to considerable variation by merely rotating the rubber sheet carrying sections 42, 44. With sections 42, 44 directly opposing the corresponding sections 12, 14, that is directly above them in spaced superimposed relation, the overall capacitance will be at a minimum inasmuch as only the adjacent edges of each pair of sections can contribute any feed-through capacitance from terminal 46 to terminal 48. On the other hand, as sections 42, 44 are rotated with respect to plate 10, each of these sections begins to overlap both of the terminal sections 12, 14, thereby providing intervening conductive linkages both having appreciable capacitive relation with each of the terminal sections. The position of maximum capacitance is that at which sections 42, 44 are rotated from the minimum capacitance position and each section 42, 44 overlaps substantially equal amounts of the terminal sections It is not necessary to have conductive sections 42, 44 identical in shape with sections 12, 14. In the form illustrated for example, sections 42, 44 are annular segments generally similar to sections 12, 14, but spaced much more closely together. Such a construction is particularly useful when the condenser is intended for high voltage operation, where the electric potential between sections 12, 14 is much higher than between sections 42, 44, so that correspondingly larger spacing is advisable. If desired, however, the spacing between sections 42, 44 can be made just as large as that between sections 12, 14.

The elastically flowable sheet 20 can be a disc of rubber that has an appreciable content of inert filler. As much as 75% filler can be used without losing the elastically flowable characteristics. Fillers such as zinc oxide, carbon, etc., are suitable. The backing member 22 can conveniently be a resin plate to which the elastically flowable sheet is cemented. The resin plate can also have the usual filler-content and may be either thermosetting or thermoplastic.

Wings 40 are shown in Fig. l as three in number. This makes a convenient arrangement inasmuch as these three wings can be positioned as alternate sides of a hexagon and can therefore be readily manipulated by the standard hexagonal rotating tools, such as socket wrenches. The gaps between the wings 40 are also suited for receiving the blade of a screw driver which can be used as a rotating tool in this manner. If desired, however, the wings can be fewer or larger in number.

Terminals 46, 48 can be made in any desired shape or configuration and are shown as slotted for more conveniently receiving connecting wires to be soldered thereto.

They can be projected in opposite directions as.

H is ceramic.

.which it is adjustedv and prevents shiftingiof; the adjust.-

shown in Fig. 1 to thereby provide lead-like extensions 'which reduce or-eliminate completely the use-of-separate connection wires.

As shown in Figs. 4 and 5 however, the terminals 46,

A48 can alternatively be.directed generally sparallel to eachzother, and awayrfromiherplane' of platenltl. ,The terminals so positioned .can :thenbexfittedthrough correspondingly; positioned openings of armounting plate 50 for example, and thenibent ,ontwatdlyasishown in Fig. 4 ortwisted as shownin Fig- 5 to lock therassembly in place. In either. of;1hese.two..mountings the. mounting platef50 provides: a. support-;.to:'withstand; the axially- ..directed forcesiusually applied zto: the condenserswhen it i is beingrotated.

.' A .feature of. the. present invention;isrtheifactirthatz the 1. :elastically flowable. pressing. 120Tv fits: closelyzcagainst: the surface 18 of. plate and .afterJtheQfashion of-.azconvention'al, gasket: provides: an pextrenielyaetfective water unperviousseal for theelectrically conductiveasections 42, Y 44. .In addition thesexconductive-.sections;.arevyieldably carried duringrotation so that they-glide.smoothlyrover pears to flow somewhat and keysitself.:intozthesmall irregularities in thesurface, 18,; especially wherexplate 10 This locks the. condenserwin the .-position to ment by vibration, shock or. inadvertent .contact ,with other articles. However an adjusting toolareadily; overcomes this locking action, zandevenyw-ithout".a.tool a forceful application of :the fingers 'JWilL su'fiice.

:-Where additional. moisture .proofing isadesired; all. exposed portions of the. dielectric surface 11 including or 1 excluding the portions covered .bysections;=12,::-14.:can be coated .with moisture resistant:material,..such-aslacquers, and resin coatings ingeneral. One-very effective protective material is astyrene-butadiene.copolymerwith very high (80-90%)v styrene:content. i';f l"he :.edges.aand

margins of plate 10. can.alsoiabevprotected by such a coating.

' For still further protection againstsmoisture,:washer 28 r can beprovided with a gasket-.56in;:contact.zrwithethe lower surface 11 of plate 10. *This'keeps.moisture'=from penetrating under the protective coatingzbyiwaysofithe eyelet aperture. Inaddition gasket 56,-xwhichtrcanabe a rubber sheet such as sheet.20, acts as .asfrictionw-ho'lder or brake for. washer. 28, keeping it from rotating when adjustments are being made. Thesurface of :the protective coating and/ or the lower face of plate 10 is.:thereby cured without'the application ofexternal pressure. One

very effective reinforcing resin is the cross-linked-epoxyline type of resin available under the trade-names Epon and *Araldite. However, other-thermosetting resins of the above class such as cast phenolics or styrene crosslinked linear copolymers are also quiteeifeetive. The reinforcing resin is best applied directly'over the soldered or sweated joint between the-terminal ends andthe electrically conductive sections 12, 14. Ifa moisture'proof coating is also used, the coating can beapplied overthe reinforcing resin.

The significance of the presentinventionwill'be more fully appreciated froma consideration that-a variable condenser, as shown in Figs. .1; 2 and 3 having anoverall diameter of Ms inch, an .overall .height' of inch and a dielectric plate '10 only 0.03 inchthick, operates very satisfactorily at 5000 volts between :terminals -46, 48.and successfully passes a 7500 -,volts .test.

, According to a different-phase of :thespresent-invention a. variable condenser can be. arranged:to:have terminal connected to movable electrode sectionsas .well-\ as one or more terminals connected to the fixed 'electrode 32,connectedasa movable terminalas' by; extending-one ofmthe sections; 42,1 44; outz-oven'the; inner edges ofuits ---tact-with-thecylindrical outer surface ofeyelet 24.

held by sheet 20 in firm C011: desired, the eyelet itself can be used as an anchorage terminal or have a terminal tab extension, and the eyelet can for this purpose be fixed in place with the drive structure arranged to rotate under head 30. One very simple technique for-1. accomplishing this result is to merely provide head 26 with extensions preferably spaced from eachother, and have these, extensions embedded in washer 28. -Any or all of the electrode sections 12, 14, 42, 44 :can be in the 'form of self-supporting foil-like strata suitably held in place. Such foils can be held against the,lower-.dielectrieface lleither bythe water-proofing coating'described above or by'a backing support such as a duplicate of .members 20,:22. .Terminals can be attached to this type of electrode'through the backing support, or where the electrodes have sufficient strength .can: benmade as extension ears integral with the electrodes. .Non-co'ated forms of electrodes,v 42, 44 can be ,-readily adheredinfplaceas by cement or by directbond- 5 ing. to a rubber, sheet 201. when thesheetis vulcanized,:for

example.

,As many .apparentlywidely.different .embodiments of this.invention.may be made Withoutdeparting from the spirit and scope hereof, it is to be, understood'thatthe invention. is\.notlimited to the specific embodiments central aperture where it is i 1 hereof, except as defined in.the appended claims. Thus .lthe plate 10 can be conventionally. ceramic with afairly low dielectricconstant, or one of the newer high dielectric. constant ceramics such as those described in the .Burnham et a. U. ,'S. patent application Serial No. 540,270,"fil'ed June 14,1944, now Patent No.@2,653,307.

What is claimed is:

' l. In-avariable condenser a ceramic dielectric disc, an electrically conductive stratum adherently'held on 'one face of the'ceramic' disc; said stratum being divided into two-"symmetrical segments; terminals separately connected to' these segments, an elastomer-disc' resiliently held against the other face of the ceramic disc, -.an electrically conductive coating: on the face' of .the elastomer disc that engages'the ceramic gdisc; saidcoating havinga shape approximately corresponding to that -ofsaid--stratum,zpivot structure rotatably holding said discs together for adjustment'to vary-the amount of'electrically conductive strata that is presented in'opposed relationto the electrically conductive coatings for adust-ing the capacitance between the terminals, said pivot structure including a" rigid backing- -plate adherently united to'the elastomer disc, central-perforations in 'the discs. and backing-plate, a \drive member -in-rotatable driving engagement with the backing plate, and an eye- -let extending' through said pe'rforations and. holding-the I "discs and plate together.

2.=-In' a variable condenser a ceramic. dielectric ldisc, an electrically conductive stratum:v adherentlynheldon one face of the ceramic disc, said stratum being divided into two symmetral segments, terminals. separately. connected to these segments, an. elastomer disc-resiliently -held-against=theother face ofthe ceramc:.disc, an electrically conductiveucoating on the faceVof-the elastomer disc that engages the:ceramic disc, said coating having a shape approximately corresponding. to that of -.said

stratum, pivot structure rotatably holding said discs -together for adjustment to varythe amount of electrically conductive strata that is presented in opposed relation to the electrically conductive coatings foradjusting-the capacitance between the terminals, 'said' pivot :struture including: arigid backing plate adherently united to the elastomer disc, central perforations in the discs and lbacking' 'plate, adrivekmemberin rotatable .drivingengagementwith the. backing plate, and an eyelet extending ;.through said perforations and holding the discs and plate together, said eyelet being a metal eyelet having a turned over head engaging, the dielectric. disc by way of insulating washer, the-,drive member is a spring metal sheet having a central-perforation, a plurality of arms-resil- .iently:extending against the, outside face of theybacking plate,; at least-one of said arms. beinghooked into::the

backing plate, and a plurality of wings extending; away "iLfI'Om the-backing plate .to provide drive 'manipulation :structure,z*the: eyeletxextending through 'the perfora-tion in the insulating washer includes an elastomeric gasket layer in engagement with the ceramic disc.

4. In a variable condenser a ceramic dielectric disc, an electrically conductive stratum adherently held on portions of one face of the ceramic disc, an elastomer disc resiliently held against the other face of the ceramic disc, an electrically conductive stratum on portions of the face of the elastomer disc that engages the ceramic disc, terminals connected to the strata portions, pivot structure rotatably holding said discs together for pivotal adjustment to bring the electrically conductive strata into varying degrees of relation with each other for adjusting the capacitance between the terminals, said pivot structure including a rigid backing plate adherently united to the elastomer disc, central perforations in the discs and backing plate, a drive member in rotatable driving engagement with the backing plate, and an eyelet extending together.

References Cited in the file of this patent Number Number UNITED STATES PATENTS Name Date Franklin Feb. 22, 1938 Ehlers Aug. 10, 1943 Ehlers Mar. 6, 1945 Minnium Sept. 14, 1948 Minnium Dec. 26, 1950 Mitchell Jan. 8, 1952 FOREIGN PATENTS Country Date Great Britain Jan. 11, 1946 

